This invention relates to photo-sensing circuits including a photo diode and a photo-current amplifier. Such a light detector system is described by R. Genesi in his U.S. Pat. No. 4,085,411, issued Apr. 18, 1978 and assigned to the same assignee as is the present invention. A light-detector in that patent employs a photo diode connected to a multistage current mirror circuit. The photo diode is connected between the input of the first stage and a DC voltage supply buss. In a copending application by W. Gontowski, Ser. No. 296,748, filed Aug. 27, 1981 and assigned to the same assignee as the present invention, a two terminal light sensor is described that may include a photo diode connected to the input of a multistage current mirror amplifier. For many uses these circuits provide current outputs that are substantially proportional to the intensity of ambient light. However, any variation in supply voltage will cause corresponding changes to appear in the output current.
It is, therefore, an object of this invention to provide a more stable photo diode and current mirror amplifier combination.
It is a further object of this invention to provide a two-terminal light sensor that is substantially unaffected by variations in the supply voltage.